Mikrotik RouterBoard RB450G

With a fast processor, gigabit ethernet, and relatively huge amounts of RAM and flash, this is a very capable device with OpenWrt installed.
With the advent of Version 18 OpenWrt, the installation process is now significantly simplified.

VLANs on the RB450G
The RB450G uses the Atheros AR8316 switch chip, which DOES support 802.1Q VLAN Trunking in OpenWrt Version 18, but does NOT support 'hybrid' or 'general' VLAN switching.
The 802.1Q Trunking capability of the AR8316 is quite capable of supporting segregated guest networks since 802.1Q Trunking allows a port to have one untagged VLAN (the 'native' VLAN1) and multiple tagged VLANs on the same port.
See the Mikrotik documentation: https://wiki.mikrotik.com/wiki/Manual:Switch_Chip_Features for an explanation of trunk, access and hybrid port capabilities for the switch chips.
That Mikrotik documentation does NOT clearly explain that Trunk ports can have one untagged and multiple tagged VLANs on one port, however Trunking is implemented and functional on OpenWrt Version 18.

RB450Gx4
If you are looking for OpenWrt support of an RB450Gx4, be aware that it uses a different CPU (IPQ4019) and switch chip (AR8327: supports 'hybrid' VLANs) than the RB450G.
The RB450Gx4 is NOT currently on the list of OpenWRT supported routers, however a WiP branch is available here. More information on the development process and the state of the branch can be found on the forum .
Pre-built images are available on the MikroTik RouterBOARD RB450Gx4 device page.

Getting Started: Refer to the Common Mikrotik Procedures for Installing OpenWrt

See Common Procedures for Mikrotik Router Boards for a general discussion of the procedures to install OpenWrt on Mikrotik RouterBoards.
The Common Procedures apply directly to the RB450G and are generally kept more up-to-date than these product-specific wiki pages, so it is a good idea to initially refer to the Common Procedures.
For example, the Common Procedures have been fully updated to reflect the considerably simplified Version 18 procedures to install OpenWrt, whereas many of these product-specific wiki's have yet to be updated.

Version 18 OpenWrt works great on the RB450G, however this wiki has not been updated for the Version 18 OpenWrt simplified installation changes.
Use the Common Procedures for Mikrotik Router Boards for detailed, up-to-date installation instructions.

Installing a New Firmware Image

OpenWrt doesn't provide a firmware image that can be written directly to the flash memory via the firmware update system in Mikrotik's RouterOS. So installing OpenWrt is a two step process that requires two separate kernel images.

You're going to need a desktop computer that has a working serial port (or adapter) and an ethernet interface. This computer will also need to have:

some kind of serial terminal software

a DHCP server; this documentation will use dnsmasq

a TFTP server; also dnsmasq

The following instructions illustrate installing Barrier Breaker 14.07, but should be easily adaptable to newer versions. For Attitude Adjustment 12.09 and previous it is required to build OpenWrt from source.

Download a netboot image for the RB450G

Boot the RB450G from the network

Connect the ethernet adapter of your desktop computer to Eth1 of the RB450G using either a straight or crossover cable. The RB450G will figure out the crossover on its own.

Manually assign an IPv4 address (anything other than 192.168.1.1, or anything in the range of IPs used in your local LAN) to the ethernet adapter on your desktop computer. Here I'll use 10.2.3.4.

Set up dnsmasq on the desktop computer.

The RB450G's bootloader apparently ignores all DHCP options, such as tftp-server or bootp-filename, normally used to instruct a netboot device how to find its image. So you need to set up dnsmasq with specific options to work around this quirk.

Copy the file openwrt-ar71xx-mikrotik-vmlinux-initramfs-lzma.elf to a clean directory like ~/tftproot/. Rename the file to vmlinux (this helps when testing other images).

dnsmasq should start in the foreground writing all its output to the terminal; you're only going to run it temporarily, and having the debugging information may come in handy.

Connect the serial port of your desktop computer to the serial port of your RB450G using a null modem cable. Start your terminal server program. The RB450G serial interface uses 8N1 with hardware flow control at 115200 bps (which is the default, but it can be configured through various means).

TIP: Try setting hardware flow control to off if you can't get to the bootloader menu (i.e. it always times out without detecting a key press). If using minicom, try minicom -o –color=on –device=/dev/ttyS#, then once minicom opens, type CONTROL A Z and find your way to disable hardware flow control. Or try screen /dev/ttyS# 115200 To figure out which ttyS device you should use, the command dmesg | grep ttyS can be helpful.

Power up the RB450G. Immediately hit any key to go to the bootloader menu:

Select p - boot protocol and then select 2 - dhcp protocol, because bootp (default) does not support dynamic address.

Select o - boot device and then select 1 - boot Ethernet once, then NAND to boot once from the network, and then boot from the nand after that.

Hit x to exit setup, the RB450G will reboot. Let the bootloader menu time out, and it should get an address via DHCP and then load the netboot image from your desktop computer. After a minute or so, you should be able to hit <enter> and get to the OpenWrt prompt.

Install the OpenWrt distribution

Don't bother configuring anything while in netboot. Any changes you make won't be written back to the original image, so they'll all be lost when you reboot anyway.

You can disconnect the ethernet connection between your RB450G and your desktop system but Do not disconnect the serial connection..

Now you'll need to establish a connection between the RB450G and the internet so that it can download the OpenWrt packages it needs for installation. Since personal LANs vary so much, I will leave this as an exercise to the reader (on my setup I chose to provide internet through the same desktop used to netboot it).

Use Eth0/PoE port to connect the RB450G to your local LAN because the netboot image will only have this port with a dynamic DHCP config. All other ports are static to 192.168.1.1, so they will require further configuration changes which are pointless at this stage given that anything you do to your system now will not be persisted;

You may need to change the dns nameserver by editing the file /etc/resolv.conf (vi /etc/resolv.conf). Replace 127.0.0.1 with 8.8.8.8 or any other public dns server. rm /etc/resolv.conf; echo nameserver 8.8.8.8 > /etc/resolv.conf will do it.

Issue the command /etc/init.d/network restart so all configuration changes are reloaded and applied;

Try ping openwrt.org and see if it works;

If networking is not okay, try editing /etc/config/network to your needs and remember to /etc/init.d/network restart after you make any changes;

There is a small quirk now, you'll have to edit wget2nand to download the right rootfs, in our case it is the DefaultNoWifi one. So sed -i 's/openwrt-ar71xx-mikrotik-rootfs.tar.gz/openwrt-ar71xx-mikrotik-DefaultNoWifi-rootfs.tar.gz/g' $(which wget2nand) will do it.

Once wget2nand finishes, you can reboot the router. This time, the router should boot from flash (since we chose try ethernet once and then nand) and give you a working OpenWrt installation that you can configure as you like.

MicroSD Card Slot

The SD card device will be called /dev/mmcblk0, with the first partition called /dev/mmcblk0p1. You will need to format the card from the command line before you can use it. For more information about setting up the card as a permanently-mounted filesystem, the USB storage instructions can be adapted, using /dev/mmcblk0* as the device names.

Some users of the RB450G state that the MicroSD slot is not designed for regular push/pull operations and microSD cards are now fit there well, plus the microSD slot is on the opposite side of the board and is not accessible in many RB450G enclosures designed originally for older RB450 model (no access hole), so when using an old RB450 enclosure you need to fully disassemble the unit to fix / add / remove the microSD card.

Specific Configuration

Switch Ports (for VLANs)

The AR7161 has two Ethernet controllers, therefore there are two interfaces, eth0 and eth1. one of these is the wan port, the other is the connection to the CPU port of the switch. The AR8316 provides the physical ports for both controllers, but they are separated internally.

Using Mikrotik NetInstall to Install RouterOS Covers the process of re-installing RouterOS after you have previously installed OpenWRT. You may need to have a copy of your RouterOS license .key file to do this (if NetInstall does not recognize your prior license)